There is a wide range of applications for spherical particles in the grain size range from 5 .mu.m to 5 mm, for example in the field of powder processing, since particles of this type can be handled without causing dust and are easy to pour. The uniformity of the particles and their narrow grain distribution permit good space filling, for example when loading press molds or chromatographic columns. They are in addition suitable as catalyst carriers.
Spherical particles made of metals or alloys are used in soldering engineering, for example, where the requirement for as narrow as possible a grain distribution is ever increasing. The interest in micro-spheres of organic materials instead of dust-producing powder is also increasing, for example in the feedstuffs sector on account of its good disability or in the pharmaceuticals industry for making pharmaceutics with depot effect.
There are also requirements for organic substances that aim at a complete and reproducible space filling, if necessary with optimum space exploitation by means of several fractions of different size but narrow grain distribution, for example in the manufacture of explosives.
There are a number of processes for manufacturing pourable particles of more or less good spherical shape, mostly based on the use of dual-substance nozzles (hollow-cone nozzles), but with a spray effect resulting not in a uniform grain spectrum, but a wide grain size distribution. A further drawback is the dust thereby generated and the formation of particles with very different properties as a result of the solidification of large and small droplets in a cooled drop distance.
To generate micro-spheres monodispersed distribution, methods are known that are based on the disintegration of liquid jets through the effect of mechanical vibrations on the liquid, where the use of periodic oscillations, for example from electro-magnetic oscillation systems, results in monodispersed droplets solidified in different ways.
Most of these methods are based on the use of aqueous solutions and other liquids at room temperature.
The solidification of droplets in these methods is mostly achieved by chemical processes such as precipitation and/or dehydration. These methods are however unsuitable for manufacturing spherical particles from liquid phases with high melting point.
U.S. Pat. No. 2,968,833 proposes a method whereby highly concentrated aqueous solutions of ammonium nitrate are converted into uniform droplets at a temperature of 140.degree. C. with the aid of vibrating nozzle systems, with the droplets solidifying into granulate particles of equal size while dropping through a cooling segment. This method can also be applied to other salts with similar chemical and physical properties, such as ammonium nitrate or area. For liquids with a high melting point, however, this method is not suitable, since no spherical particles are formed at high temperatures or the particles stick together in the cooling segment.
German patent 27 25 924 also described a method of diffusing melted substances under vibration through a nozzle and generating spherical particles by solidification of the droplets in a cooled drop distance. A major drawback of this method is that cooling and solidification of the droplets takes place in a temperature gradient, which can only be controlled with difficulty at higher temperatures in particular. Here too, the particles stick together in the cooling segment at higher temperatures.